Typically, photosensitive articles such as photoresists are prepared using a photosensitive resin solution or film as the resist material. Conventional photosensitive resins are available as solutions prepared in organic solvents or in the form of film produced from such solutions (in organic solvent).
Organic solvents have also been used in the past in the development process following exposure to light. In recent years, in response to health, safety and environmental concerns, diluted aqueous alkaline solutions have replaced organic solvents as the developer solutions. However, health, safety and environmental concerns remain to the extent that organic solvents are still used in the resin solution, because it is still not possible to avoid evaporation of the organic solvent during coating of the resist, drying of the coated resist, or processing into a film.
In Japanese Kokai Patent, SHO 54-91585 (1979), an attempt was made to address these problems using a photosensitive resin composition made of a water-dispersible latex and water-soluble (or water-dispersible) unsaturated compound. However, such a system is undesirable due to the risks associated with working in aqueous systems during etching or plating operations because of the high hydrophilic property of the water-soluble unsaturated compound. Therefore, use of a water-insoluble unsaturated compound is preferred. It has been, however, difficult to mix the water-insoluble unsaturated compound stably with a water-dispersible latex.
In U.S. Pat. No. 5,045,435, the aforementioned problems were addressed by neutralizing a part of the acid of the water-insoluble carboxylated(meth) acrylate latex with inorganic alkali or amines, to stabilize the composition and perform rheological adjustment during coating. Although a stable composition can be obtained by such method, the use of such a composition is undesirable due to the production of noxious fumes during resist preparation due to vaporization of amines and the effect that inorganic alkali can have on electronic equipment.
It is, therefore, a general object of the present invention to provide a process for preparing a waterborne photosensitive resin composition, that provides a stable mixture of an aqueous polymer emulsion and a water-insoluble unsaturated compound.
It is a further object of the present invention to provide a waterborne photosensitive resin composition, that when used to make a resist film, avoids the risks associated with organic solvents such as splashing during resist processing.